1. Field of the Invention
The present invention relates to an elevator car position detecting apparatus for detecting the position of an elevator car when the car is near one of the ends of the path of the elevator.
2. Description of the Prior Art
Japanese Patent Application Laid-open No. 62-280174 describes an elevator car position detecting apparatus as illustrated in FIG. 4. Referring to the figure, arms 2a to 2e are horizontally projected from a wall 1 of the path along which an elevator car 6 is moved up and down. The arms 2a to 2e are arranged vertically in order of length. More specifically, the lowest arm 2a is the shortest, and the uppermost arm 2e is the longest. A cam 3 is fixed to the end portions of the arms 2a to 2e and has inclined portions 3a to 3d. A switch 5 is attached to the car 6.
The switch 5 comprises: a roller 50 which is associated with the cam 3 as the car 6 ascends; a lever 51 which turns about a fulcrum 52 when the roller 50 is associated with the cam 3; springs 52a and 52b connected to a lower portion of the lever 51 so as to maintain the lower portion of the lever substantially in the vertical posture when the roller 50 does not receive an external force; and switch box 54 containing switches (described below) which are operated as the lever 51 turns.
Components contained in the switch box 54 will be described with reference to FIG. 5. The lever 51 is connected at the lower end to a horizontal bar 53. Contacts 51a to 51d are connected to the horizontal bar 53. A contact 54a faces the contact 51a, spaced from the contact 51a by an air gap g1. Similarly, contacts 51b to 54d face the contacts 53b to 53d, spaced by air gaps g2 to g4, respectively. The size relation of the air gaps g1 to g4 are: EQU g1&lt;g2&lt;g3&lt;g4
The four pairs of contacts, 51a and 54a to 51d and 54d, form four separate switches 55a to 55d.
The operation of the above-described conventional elevator car position detecting apparatus will be described.
When the car 6 is far from the top end of the path and therefore the roller 50 is not associated with the cam 3, the lever 51 assumes a vertical posture (as shown in FIG. 5) and all the switches 55a to 55d are off. When the roller 50 becomes associated with the inclined portion 3a of the cam 3 as the car 6 ascends, the lever 51 turns in the direction indicated by the arrow R in FIG. 5 and thus connects the switch 55a. The switch-on signal thus generated is sent to a control unit (not shown), thus informing that the car has reached the inclined portion 3a. As the car 6 further ascends so that the roller 3a is associated with the inclined portion 3b, the lever 51 further turns in the direction indicated by the arrow R, thus connecting the switch 55b. In the same manner, as the roller 50 becomes associated sequentially with the inclined portions 3c and 3d, the lever 51 further turns to sequentially connect the switches 55c and 55d. In this manner, the switch-on signals generated by the switches 55a to 55d inform the control unit that the car 6 has reached the corresponding positions.
Then, as the car 6 descends from the top position, the switch 55d is first disconnected, and the switch 55a is last disconnected. The control unit thus monitors the position of the car 6.
Although the above description has been made with reference to the case where the car 6 is near the top terminal floor, it will be easily understood, without further description, that the position of the car 6 can be monitored in a similar manner when the car 6 is near the bottom terminal floor.
The above Japanese Patent Application Laid-open No. 62-280174 also describes a position detecting apparatus comprising: a detector which is attached to an elevator car and has a light emitter and a light receiver; and a stepped light-shielding plate which is attached to the path of the elevator car and insertable into a gap between the light emitter and the light receiver without contacting either the light emitter or receiver. The patent application further states that such a position detecting apparatus can also be achieved by utilizing magnetism, for example, employing a magnetism-shielding plate instead of the light-shielding plate.
However, because the above-described conventional detecting apparatuses employing cams connected to the paths of the elevator cars detect the position of an elevator car on the basis of the positions of the inclined portions of the cam, the size of the gap between the elevator car and the wall of the path significantly affects the precision of the position detection, thus requiring precise installation and adjustment of the elevator, which is not easy. Even if precise installation and adjustment is achieved, the gap size varies as the elevator is used. In several years, the detection precision deteriorates to such a level that re-adjustment is required. Further, the conventional apparatus produces noise when the roller contacts the cam. The noise problems can be eliminated by a non-contact position detecting apparatus. However, both the contact and non-contact types require as many cam surfaces or shielding plates as the positions to be detected, and as many detection elements, e.g., switches. To increase the number of positions to be detected, the number of these components must be proportionally increased.